Method for making laminated pressure vessels



Apfiii 1967 T. J. REINHART, JR 3,

METHOD FOR MAKING LAMINATED PRESSURE VESSELS Or1gina1 Filed Dec. 4, 19621 N VEN TOR.

r/wooaeazzf/n/lw 7pm. BY M Patented Apr. 11, 1967 3,313,664 METHGD FORMAKENG LAMINATED lRESSURE VESSELS Theodore J. Reinhart, J12, 4116Woodedge Drive, Bellhrook, Ohio 45365 Original application Dec. 4, 1962,Ser. No. 242,335, new Patent No. 3,207,352, dated Sept. 21, 1965.Divided and this application Aug. 12, 1963, Ser. No. 301,682 4 Claims.(Cl. 156-455) The present application is a division of my copendingapplication Ser. No. 242,335, filed on Dec. 4, 1962, now United StatesPatent No. 3,207,352.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without the payment to me ofany royalty thereon.

This invention relates generally to a method for making pressure vesselsand, more specifically, to the making of laminated pressure vessels foruse under extremely high pressures. Furthermore, pressure vessels madein accordance with this invention may be either so-called closed vesselsor open vessels such as rocket motor cases.

It has been well established that when the wall thickness of a pressurevessel approaches of its radius, the thin wall pressure vessel formulasand membrane theory are no longer applicable. Thick-wall theory must beapplied in the design of such vessels and structures.

It is well known that when a thick wall pressure vessel is internallypressurized, a stress gradient is set up in the wall. The inducedtensile stresses are a maximum at the inside radius and diminish towardthe outside radius. Likewise, when such a pressure vessel is subjectedto external pressure, the compressive stresses progressively increasefrom the outer to the irmer radius of the vessel.

In the conventional thick-wall homogeneous or laminated vessels, thisstress gradient has been ignored and the vessels designed to limit themaximum stress to that which the inner layer of material may withstand.This, by necessity, results in a relatively inetficient use of materialand a heavy vessel. Not only are needlessly heavy pressure vessels moreexpensiv to fabricate, but in many applications such as found onairplanes and space craft, such excess weight is extremely detrimental.

This invention provides a simple and effective solution to thethick-wall, stress gradient roblem. Pressure vessels made in accordancewith this invention consist of filament or tape wound contiguous orlaminated shells; being of so-called thin layer construction, each shellfrom the inner to the outer shell being formed of a H material having agreater modulus of elasticity than the preceding shell. The actualdimensional design of th pressure vessel may be trial and error, or inaccordance with formulas developed for various shaped vessels.

When a pressure vessel made in accordance with this invention ispressurized, the greater stiffness of tie outer layer causes it toabsorb stress at a greater rate than its immediately adjacent innershell. Furthermore, the greater stiffness of the outer layers tend torestrict the stress absorption of the inner layers. The inter-shellinteractiombeing in direct opposition to the stress gradient of a thickwall structure, tends to counteract or negate the stress gradient in theconventional thick wall vessel.

When a pressure vessel made in accordance with this invention issubjected to external pressure, as when used at depths in the ocean, theinteraction between shells would, in like manner, serve to level out thecompressive stress gradient induced in the wall of the vessel.

A vessel made in accordance with this invention, by the proper selectionof materials and shell thickness, may be made to have a wall having asubstantially uniform stress level throughout. Such a vessel may be madewith the minimum amount of material working at maximum efficiency.

The primary object of this invention is to provide a method for makingpressure vessels in which all the materials comprising the walls aresubstantially stressed.

Another object of this invention is to provide a method for making alaminated pressure vessel corresponding to a conventional thick-wallvessel and in which each shell is carrying a proportionate part of thestress resulting from the pressure acting on the vessel.

A further object of this invention is to provide a method for making alaminated pressure vessel in which the various shells may be made ofmaterials each having a different modulus of elasticity in order tosecure better stress distribution within the walls of the vessel.

Yet another object of this invention is to provide a method for makingthe lightest possible high pressure vessel, by efficiently utilizing thematerials comprising the vessel.

A still further object of this invention is to provide a method formaking a high strength, lightweight pressure vessel having a pluralityof laminated or contiguous shells which are seamless and in which thematerials comprising the walls are substantially and more or lessuniformly stressed from either internal or external pressure.

Additional objects, advantages and features of the invention reside inthe construction, arrangement and combination of parts involved in theembodiments of the invention as will appear from the followingdescription and accompanying drawings, wherein:

FIG. 1 shows a spherical vessel in partial section as representative ofa closed pressure vessel made in accordance with this invention, and

FIG. 2 shows in partial section an open end vessel such as used onrocket motors, as representative of open end pressure vessels made inaccordance with the invention.

Referring to FIG. 1, which is representative of closed vesselstructures, the pressure vessel referred to generally as vessel 10 isshown as having three contiguous shells; the outer shell 12, theintermediate shell 14 and the inner shell 16. Although three shells areshown, any number of shells greater than one may be used within thescope of the invention. Each shell may be made of any suitable materialin the form of filaments or tapes and wound in a manner well known tothe art. Suitable bonding materials may be used during construction, andthe vessel so formed may be cured as dictated; the bondin and curingprocesses being well known to the art and not constituting part of thisinvention.

If desired, a strain-absorbing elastomeric coating 18 and 18a may beapplied between shells. Such coating may be made of 'butyl rubber, forexample. Such coating has little compressibility and serves to absorbstrain dilferentials between the shells.

In many applications, depending upon the gases to be contained withinthe vessel, and permeability of the vessel, the vessel so formed will becompletely satisfactory. In other applications, it may be desirable oreven necessary to use an inner liner 20 which may be metallic or of lowpermeable non-metallic material. If desired, the completed vessel may becoated with a moisture barrier or protective coating 22.

The vessel is provided with suitable connective openings such as opening24. Such openings, which are usually threaded or flanged, are notclaimed as part of this invention and may be built into the vessel inmanners well known to the art.

The tabulation below, which in no way limits the materials Which may beused in the construction of vessels in accordance with this invention,is intended to show how materials for the various shells may be selectedbased upon a graduated modulus of elasticity. Likewise, there is notlimitation stating that all shells should be constructed from materialsin the same group. For example, a vessel could readily "be made havingone shell of glass filaments, one of metal filaments and one of organicfilaments.

GLASS FILAMENTS Designation Elastic modulus, -p.s.i. E Glass 10.5)( 994Glass 125x10 YM31A Glass 16.0 X 10 METAL FILAMENTS Titanium 17 X 10Steel 30x10 Molybdenum 50x10 ORGANIC FILAMENTS Grams/denier Nylon 6ODacron 80 Fortisan 100 Ht-l 140 A second embodiment of the invention isshown on FIG. 2 which is representative of open pressure vessels such asused for example on a missile motor case. The vessel depicted by FIG. 2may be made in accordance with the method used in making the closedpressure vessel previously described. Accordingly, like elements on bothfigures are designated by like numerals.

Pressure vessels in accordance with this invention may be made bywinding onto a suitable mandrel. With vessels which do not use ametallic inner liner, such a mandrel may be cast or Otherwise formed oflow temperature metal or alloys as for example Woods metal. After thevessel is completed, if a metal mandrel was used, the metal is meltedand poured from the vessel through one of the openings.

With vessels using a metallic inner liner, the mandrel may be formed byfilling the liner with liquid metal which is then allowed to solidify.After the vessel is formed, the mandrel is again liquefied and pouredfrom the vessel.

It is to be understood that the embodiments of the present invention asshown and described are to be regarded as illustrative only and that theinvention is susceptible to variations, modifications and changes withinthe scope of the appended claims.

I claim:

1. The method of forming a filament wound laminated pressure vessel,having at least one opening and at least two contiguous shells,comprising the steps of:

(a) constructing a first heat-curable shell from a first filament and a'bonding material, said first filament being wound onto a preformedmandrel made from a solidified material that is liquefiable; then,

(b) constructing a succeeding heat-curable shell from a second filamentand a bonding material, said second filament being wound onto said firstshell, said second filament having a higher modulus of elasticity thansaid first filament, the vessel formed by said shells being providedwith said one opening; then,

(c) "heat curing the shells; and then,

((1) liquefying said mandrel and pouring said liquid from said vesselthrough said one opening.

2. The method of forming a filament wound laminated pressure vessel,containing a preformed metallic. inner liner having at least one openingand having at least two contiguous shells, comprising the steps of;

(a) constructing a first heat-curable shell from a first filament and abonding material, said first filament being Wound onto a preformedmetallic inner liner filled with a solidified material that isliquefiable; then,

(b) constructing a succeeding heat-curable shell from a second filamentand a bonding material, said second filament being wound onto said firstshell, said second filament having a higher modulus of elasticity thansaid first filament, the vessel formed by said liner and shells beingprovided with said one opening; and then,

(c) heat curing the shells; and then,

(d) liquefying said solidified material in said liner and pouring theliquid from said vessel through said one opening.

3. The method of forming a filament Wound laminated pressure vessel,having at least one opening and at least two contiguous shells with anelastomeric coating between adjacent shells, comprising the steps:

(a) constructing a first heat-curable shell from a first filament and abonding material, said first filament being wound onto a preformedmandrel made from a solidified material that is liquefiable; then (b)applying a coating of elastomeric material onto the surface of saidfirst shell; then,

(0) constructing a succeeding heat-curable shell from a second filamentand a heatcurable bonding material, said second filament being woundonto said first shell, said second filament having a higher modulus ofelasticity than said first filament, the vessel formed by said shellsbeing provided with said one opening; then,

(d) heat curing the shells; and then,

(e) liquefying said mandrel and pouring said liquid from said vesselthrough said one opening.

4. The method of forming a filament wound laminated pressure vessel,containing a preformed metallic inner liner having at least one openingand at least two contiguous shells with an elastomeric coating betweenadj acent shells, comprising the steps:

(a) constructing a first heat-curable shell from a first filament and abonding material, said first filament being wound onto a preformedmetallic inner liner filed with a solidified material that isliquefiable; then,

(b) applying a coating of elastomeric material onto the surface of saidshell; then,

(c) constructing a succeeding heat-curable shell from a second filamentand a bonding material, said second filament being wound onto said firstshell, said second filament having a higher modulus of elasticity thansaid first filament, the vessel formed by said liner and shells beingprovided with said one opening; and then,

(d) heat curing the shells; and then,

(e) liquefying said solidified material in said liner and pouring theliquid from said vessel through said one opening.

References Cited by the Examiner UNITED STATES PATENTS 2,337,247 12/1943Kepler 29-446 X 2,359,446 10/1944 Scudder 29446 X 2,744,043 5/1956Ramberg 156l55 2,786,007 3/1957 Chew 156155 EARL M. BERGERT, PrimaryExaminer.

M. L. KATZ, Assistant Examiner,

1. THE METHOD OF FORMING A FILAMENT WOUND LAMINATED PRESSURE VESSEL,HAVING AT LEAST ONE OPENING AND AT LEAST TWO CONTIGUOUS SHELLS,COMPRISING THE STEPS OF: (A) CONSTRUCTING A FIRST HEAT-CURABLE SHELLFROM A FIRST FILAMENT AND A BONDING MATERIAL, SAID FIRST FILAMENT BEINGWOUND ONTO A PREFORMED MANDREL MADE FROM A SOLIDFIED MATERIAL THAT ISLIQUEFIABLE; THEN, (B) CONSTRUCTING A SUCCEEDING HEAT-CURABLE SHELL FROMA SECOND FILAMENT AND A BONDING MATERIAL, SAID SECOND FILAMENT BEINGWOUND ONTO SAID FIRST SHELL, SAID SECOND FILAMENT HAVING A HIGHERMODULUS OF ELASTICITY THAN SAID FIRST FILAMENT, THE VESSEL FORMED BYSAID SHELLS BEING PROVIDED WITH SAID ONE OPENING; THEN, (C) HEAT CURINGTHE SHELLS; AND THEN, (D) LIQUEFYING SAID MANDREL AND POURING SAIDLIQUID FROM SAID VESSEL THROUGH SAID ONE OPENING.